BackgroundThe B-10, the
first of the modern all-metal
monoplane bombers to be produced in quantity, featured such innovations
as internal bomb storage, retractable landing gear, a rotating gun
turret, and enclosed cockpits, that served with the USAAC in 1933-1936
period until replaced by the Boeing B-17 Flying Fortress.

In 1936, the B-10 design was sold for export as the model 139W. 189 B-10 bombers were sold to foreign customers.
120 of these went to the Netherlands East Indies (NEIAF). In the
late later 1930's and during WWII, China and the Netherlands flew
export versions in combat against Japan. Also, 3 B-10s served with
the Philippine Army Air Corps. Argentina bought 35 Martin 139Ws, including 12 for the Argentine Navy